Thomas has conceded the point – “Thanks for catching my errors!” – and this article has vanished, to be replaced by one on Mercury. A screenshot of the original is available here.
Today’s DpSU – Saturn Moon’s Space Geyser Should Not Exist – is an example, among other things, of Brian Thomas taking a minor detail from a science news article (here, Enceladus Plume is a New Kind of Plasma Laboratory) and running off on a creationism-related tangent. His entire argument consists of these two paragraphs:
Enceladus loses “about 200 pounds of water vapor per second,” which roughly equates to three tons per year. Enceladus weighs over 100 quadrillion tons and supposedly formed billions of years ago. The plume provides an opportunity to cross-check its old-age assignment.
Assuming that the small Saturnian satellite has always issued the same amount of material at the same rate as it does today, then it would have completely unspooled itself in about 35 million years. Why is it still so active?
The full quote includes a metric value:
About 200 pounds (about 100 kilograms) of water vapor per second – about as much as an active comet – spray out from long cracks in the south polar region known as “tiger stripes.”
Now, I have three important problems with Thomas’ claim:
- He makes two flawed assumptions: first, that “the small Saturnian satellite has always issued the same amount of material at the same rate as it does today,” second, the “always” part. The importance of the first is that the moon need not have outputted the same amount for its entire existence – it could, for example, output more and more as it gets smaller, having (say) a smaller gravitational force pulling on the water. The second is that it is not being claimed that Enceladus has been outputting continuously for the entire age of the solar system or even its own existence, hence this does not put an upper limit on the age of anything (except possibly – though not really, see below – the geysers themselves).
- The calculation is presented as if it showed how long the geysers could have been going, but instead calculates how long, at that rate, the geysers will last into the future. It tells you how long until the balloon will fully deflate, so to speak, but not how long it has already been doing so.
For example, if we assumed both that the moon “has always issued the same amount of material at the same rate as it does today,” and that it was originally the size, say, of Titan, we can calculate how long it would have taken for it to ‘deflate’ to its present mass.
To do this we take the mass of Titan and subtract the mass of Enceladus to get the difference, i.e. the mass that must have been lost. This comes out to a little more than 1 × 1023 kg (we’re using metric here, because its easier), not noticeably smaller than the full mass of Titan as that moon more than a thousand times heavier than its icy neighbour.
Divide this, then, by 100 to get the number of seconds this would take at the 100 kg per second rate: this gives around 1 × 1021 seconds. This then converts to…
More than 40 trillion years.
- You may have noticed that this new figure is rather large: if Titan is a thousand times more massive than Enceladus, why do we get a number that is a million times larger? The answer is that Brian Thomas has apparently made a mistake that has thrown off his calculations by a factor of a thousand.
Lets work it out for ourselves (or you can use the second handy widget provided). The mass of Enceladus is approximately 1 × 1020 kg, which when divided by 100 again gives us 1 × 1018 seconds, as you might expect. This figure translates to not “about 35 million years” but about 35 billion years.
There’s no problem for a universe older than 6000 years here.
Back to the drawing-board, methinks. I’ve let them know about the error – as it is inarguable and ruins the article completely it will be interesting to see what they do.